Radio receiver



April y 1938- c. J. VAN LOON ET AL 2,114,025

RADIO RECEIVER Filed April 21, 1934 INVENTOR Owen JA/V 14w L00 ATTORNEY Patented Apr. 12, 1938 2,114,025 RADIO RECEIVER Carel Jan van Loon and Johannes A. J. Bouman, Eindhoven, Netherlands, assignors to Radio Corporation of America, a corporation of Delaware - Application April 21, 1934, Serial No. 721,724

. 1 In the Netherlands April 29, 1933- 8 Claims.

This invention relates to radio receiving sets comprising a change-over device by means of which it is possible to adjust to different ranges of wave lengths Usually such a change-over 5 device consists of a switch by which part of the tuning coils can be short-circuited.

It has been found that changing-over to another range of wave lengths entails not only a modification of the tuning but also of the average sensitiveness of the receiving apparatus.

The latter modificationis undesired and according to the invention it is avoided by using a wave length switch which is mechanically coupled with a device for modifying the amplifica- 15 tion factor of the apparatus. In this manner it is possible to modify, for instance, the amplification factor of one or more of the tubes simultaneously with the adjustment to another range of wave lengths in such a manner that in total the average amplification of the apparatus for eachrange =,of wave lengths is the same. i I The invention will be more clearly understood by reference to the accompanying drawing g representing by way of example, one form of construction thereof.

Of theradio receiving apparatus represented in the drawing only one of the high frequency amplifying tubes l is shown whose input circuit 30 comprises two tunable circuits 2 and 3 which are coupled together. .In the circuit 2 are inserted a condenser 4 and two coils 5 and '6, the circuit 3 comprising the coils I, 8 and a tuning condenser 9; The circuits 2 and 3 are 5 capacitively coupled as shown. The grid bias of the tube I is obtained by means of resistances II, I2, l3 which are connected to a source of energy. Furthermore switches I4 and I5 are provided by which the coil 6 and resistance I2 40 and the coil 8 respectively can be short-circuited.

If it is desired to tune to a frequency of the long wave-range the switches I4 and I5 which are mechanically coupled together are opened. The value of the grid bias of the tube I is deter- 45 mined by the ratio between the values of the resistance II and the resistances I2 andv I3 which form a potentiometer across a source of grid bias.

This source of bias may have either a fixed 50 value or be adjustable. In the case under review the source of bias consists of the voltage set up through the resistance II and part of the resistance II. The value can be controlled by hand by displacing the contact I6 over the 55 resistance I1, of which the most positive point I8 is connected to the cathode of the tube I. In this case the grid bias of the tube l amounts to part of the tension set up between the points It and I8 which part is determined by the potentiometer II, l2, l3.

When reception of short waves is desired the switches 14 and I5 are closed, owing to which not only part of the inductance of the circuits [and 3 is short circuited but also the resistance I2, i. e. part. of the potentiometer connected across the source of bias is short circuited in such a manner that the bias of the tube I becomes less negative so that the amplification factorof this tube increases. This is desirable since due to the short circuiting of'part of the 15 tuning coils the sensitivity of the apparatus has decreased. This decrease of the sensitivity is compensated by an increase of the sensitivity resulting from the increase of the amplification factor of one of the tubes.

If the receiving set is so constructed that changing-over from the long-Wave to the short wave range produces an increase of the average sensitivity of the set, a similar circuit arrangement may be used, in which, however, not part of the resistance provided between the grid of the amplifying tube and the positive side of :the source of bias, but part of the resistance 'provided between the grid and the negative side of the source of bias is short circuited.

We claim:

1. In a tunable amplifier of the type including at least one electronic tube and a change-over device for adjusting the amplifier to receive signals of different frequency ranges, the method of maintaining the amplifying characteristics of the amplifier substantially constant for all the frequency ranges which includes the step of automatically modifying the amplification characteristics of the electronic tube when changing 40 from one frequency range to another.

2. In an amplifier system in combination, a vacuum tube amplifier, a tunable input circuit therefor, a change-over device for adjusting the tunable circuit so as to tune to different fre- 46 quency ranges, resistance means for controlling the bias voltage applied to the signal input grid of said tube and a single means for operating both said device and the last named means.

3. In a tunable amplifier of the type including 50 at least one electronic tube, an associated tuning circuit including an inductance coil and a change-over device for adjusting the amplifier to receive signals of different frequency ranges, the change-over device acting to short-circuit cation characteristics of the electronic tube to increase its amplifying power when changing from one frequency range to a higher frequency range.

4. In radio receiving apparatus of the type" provided with a tunable circuit and an associated electronic tube, said tube having an anode, a

cathode and at least one grid electrode, said grid electrode being biased with respect to the cathode to determine thereby the sensitivity of therreceiv-v ing apparatus, means for adjusting the tunable circuit soras toladaptiit to tune to different ranges of'waveslengths whereby the receiver may be utilized to :rec'eivesignals transmitted on widely separated frequencies; means 'for varying the biasing potential applied to the grid electrode to therebychange: the sensitivity characteristics of theaelectronicftube. and single means for operating'tboth'the'biassvarying means and the tunable circuit:adjus'tingcmeans simultaneously and in s'uchuarway thattha-zbiasing potential applied to thelele'ctronic tube for-reach frequency range to which the. tunable circuit is adjusted by operationxof' the single ,means affects the operating characteristics'of the electronic tube so that the sensitivity of the receiving apparatus is predetermined for each of the different frequency ranges.

5. In radioreceivingapparatus of the type providedxwit'h at :least'onei electronic tube having a cathode, an anode andagrid electrode, a tunable circuitnonnected between the cathode and the grid electrode, operable means for adjusting the tunable circuit soirasoto adapt it to tune the receivingtapparatus. through different ranges of wave lengths, operable means for applying a negative 'potential to the: control electrode of the tube with respect to "the; cathode thereof, means foroperatingthezfirst named operable means and means controlled by the last named means operating the second named operable means to thereby vary the potential applied to said control electrode with changes in the adjustment of the tunable circuit.

6. In a tuned radio frequency system adapted to operate over a plurality of frequency hands, a pair of coupled tunable circuits, each thereof comprising an inductance-coil and a tuning condenser, means to short-circuit a portion of said inductance coils whereby the frequency range over which the tuning condensers tune their respective coils is changed from a lower to a higher one of said frequency bands, an electronic tube 'amplifier'provided with an anode, a cathode and at least one grid electrode, said tube being coupledrto one of said tunable circuits, means for varying. the amplification characteristics of said electronic tube amplifier and a single means for operating the short-circuiting means and the means'for varying the amplification charcteristics of said electronic tube simultaneously in such a Way that the amplification power of the tube is increasedv upon changing from said lower to said higher frequency range.

'7. In a tunable radio frequency amplifier circuit of the type which is provided with a changeover device for adjusting the amplifier circuit to tune to different frequency ranges, operable means for modifying the amplification characteristics of the amplifier circuit and a single means for operating the change-over device and said operable means simultaneously so as to automatically increase the amplifying ability of the circuit when said circuit is adjusted to tune through the higher frequency range.

8. A multi-range radio frequency amplifier of the type which is provided with a tuning circuit including an inductance coil and means for shortcircuitinga portion of the coil, and with a bias resistor said' amplifier' being characterized by that a portion of the bias resistor is also short-circuited by the same means which is utilized to short-circuit the portion of the inductance coil above mentioned.v

CAREL JAN VAN LOON. JOHANNES A. J. 

